Predicting and Storing Unutilised Irrigation Orders for Environmental Benefit Matthew James Berrisford Submitted in total fulfillment of the requirements of the degree of Doctor of Philosophy May 2008 Department of Civil and Environmental Engineering The University of Melbourne Abstract Regulation of river systems and the development of irrigated agriculture have contributed to a shift in the seasonality of flow of a large number of river systems. The River Murray, Australia is one such river. The well documented side of a change in seasonality of flow is the decreased incidence of winter and spring flood events; a lesser known impact and a focus of this research is the increased incidence of summer flooding. One location where the incidence of increased summer flooding is of great importance is the Barmah-Millewa Forest (B-MF) which surrounds the Barmah Choke on the River Murray. The B-MF is located a small distance downstream of Yarrawonga Weir, a major irrigation diversion point for Murray Irrigation Limited and Goulburn-Murray Water. Yarrawonga Weir is located four days water travel time downstream of Lake Hume. Lake Hume is the storage point for these two irrigation authorities. The process for irrigators to receive water in these two districts is to place an order, water is then released from storage and they receive water four days after the placement of the order. If there is rainfall during the four day lag irrigators can reject or cancel their order; this type of event has previously been termed a ‘rain rejection event’. Rejected water remains in the River Murray continuing to flow downstream, potentially causing unseasonal flooding of the B-MF. Due to the lack of available data on rejection, a substitute data set referred to as unutilised irrigation orders (UIO) has been used throughout this research. This research firstly seeks to qualify and quantify the link between UIO and rainfall and then between UIO and unseasonal flooding of the B-MF. The research then moves to investigate storing UIO in on-farm or en-route water storages to reduce the incidence and occurrence of unseasonal flooding of the B-MF, using part of the Murray Irrigation Limited system as a study area. The storage assessment is based on the storages ability to capture and reuse UIO. To undertake the above investigation irrigators were initially surveyed, via an interview questionnaire regarding their order and rejection behaviour. Following this, Multiple i Linear Regression analysis was used to explore a link between UIO and rainfall and between UIO and unseasonal flood events of the B-MF. To investigate different storage options for UIO the model Options AnalysiS in Irrigation Systems (OASIS) was extended to include a process for placing an order and rejection. The major findings of this research are that unseasonal flooding of the B-MF can be linked to UIO but there are other more significant factors. UIO were found to be linked to the previous day’s UIO, rainfall and the order volume placed four days prior. From the scenario assessment little difference was found between the performance of on-farm water storages and en-route water storages. Thus, factors other than the ability to capture rejected water and ability to reuse this water for irrigation need to be considered by the irrigation authority when selecting a method for capturing and storing UIO’s. These factors could include other management and operational factors. ii Declaration This is to certify that i. the thesis comprises only my original work towards the PhD, ii. due acknowledgement has been made in the text to all other materials used, iii. the thesis is less than 100,000 words in length, exclusive of tables, maps, bibliographies and appendices. iii Acknowledgements Throughout this work I have received support from numerous people and organisations. Firstly, I would like to thank Nicolas Roost for volunteering his time and energy to assist with developments and alterations made to the OASIS model. His assistance and enthusiasm with this work was unexpected, invaluable and greatly appreciated. I have also received considerable support, feedback and guidance from my supervisors Hector Malano and Robert Argent. The staff at Murray Irrigation Limited in particular David Watts have provided invaluable assistance on the operation of the Murray Irrigation supply system. The Co-operative Research Centre for Irrigation Futures (CRCIF) who provided a scholarship, operating budget and a forum to link with both industry and other researchers. I would also like to thank my colleagues, family and friends for their friendship and support away from study. iv Table of Contents ABSTRACT................................................................................................................................. I TABLE OF CONTENTS ..........................................................................................................V LIST OF FIGURES.................................................................................................................IX LIST OF TABLES................................................................................................................... XI LIST OF TABLES................................................................................................................... XI LIST OF ACRONYMS AND ABBREVIATIONS ............................................................ XIII 1 INTRODUCTION................................................................................................................1 1.1 THE MURRAY DARLING BASIN .........................................................................................1 1.2 MURRAY IRRIGATION LIMITED ........................................................................................4 1.3 IRRIGATION ORDERS .........................................................................................................5 1.4 REJECTIONS........................................................................................................................5 1.5 FLOW CHANGES AND ECOLOGICAL CONSEQUENCES.......................................................6 1.6 THE RIVER MURRAY .........................................................................................................7 1.7 THE BARMAH-MILLEWA FOREST.....................................................................................9 1.8 WATER STORAGES...........................................................................................................11 1.9 RESEARCH QUESTIONS....................................................................................................12 1.10 RESEARCH OBJECTIVES ................................................................................................12 1.11 THESIS OUTLINE ............................................................................................................12 1.12 ORIGINAL CONTRIBUTIONS ..........................................................................................14 2 THE MURRAY IRRIGATION SYSTEM.......................................................................15 2.1 MURRAY IRRIGATION LIMITED ......................................................................................15 2.1.1 AGRICULTURAL LAND USE .............................................................................................16 2.2 CLIMATE DATA.................................................................................................................19 2.2.1 WATER ALLOCATION......................................................................................................21 2.3 OPERATION OF THE MURRAY IRRIGATION SYSTEM .....................................................23 2.4 THE STUDY AREA.............................................................................................................26 2.4.1 CALCULATION OF UIO ...................................................................................................28 3 UNUTILISED IRRIGATION ORDERS AND UNSEASONAL FLOODING OF THE BARMAH-MILLEWA FOREST............................................................................................33 3.1 SURVEY QUESTIONNAIRE ................................................................................................35 3.1.1 MIA RESULTS .................................................................................................................36 3.1.2 GENERAL RESULTS .........................................................................................................37 3.1.3 NON-RICE CROPS RESULTS .............................................................................................40 3.1.4 RICE CROP RESULTS........................................................................................................43 v 3.2 REGRESSION ANALYSIS ...................................................................................................45 3.3 MULTIPLE LINEAR REGRESSION ....................................................................................47 3.3.1 IDENTIFYING THE BEST MLR MODEL .............................................................................48 3.4 MLR INVESTIGATION OF FLOWS AT TOCUMWAL.........................................................50 3.4.1 CALIBRATION AND VALIDATION OF THE MLR MODELS.................................................52 3.4.2 MLR MODEL INVESTIGATION.........................................................................................54 3.4.3 IDENTIFYING THE BEST MLR MODEL FOR FLOWS AT TOCUMWAL ................................57